Ask Brock Turner or his father what made him sexually assault an unconscious woman behind a dumpster on the Stanford University campus, and they’ve got a ready answer: alcohol.

“I know I can impact and change people’s attitudes towards the culture surrounded by binge drinking and sexual promiscuity that protrudes through what people think is at the core of being a college student,” Turner wrote, seeking leniency from the judge. “Brock was desperately trying to fit in at Stanford and fell into the culture of alcohol consumption and partying,” his father wrote in his own letter.

The idea that alcohol makes people more aggressive or more likely to misunderstand consent is widely believed. But in reality, the facts just don’t support it.

Men who are likely to commit sexual assault will do so drunk or sober. (Women can be aggressors and men can be targets; we’re focusing here on the vast majority of assaults, in which men are the aggressors and women the targets.) “Men who commit sexual assault when drinking alcohol are similar to men who commit sexual assault when sober in most aspects of their personality and attitudes,” found one meta-analysis (a study of many studies). Factors like hypermasculinity and belief in rigid gender norms were what mattered, not alcohol consumption.

And it’s not that men who assault women are too drunk to know better, or that there was a miscommunication. Researcher Kate Graham and her team studied bar behavior and found that unwanted sexual aggression was often “intentional sexual invasiveness and unwanted persistence rather than misperceptions in sexual advances.”

Here’s the truth: There is a connection between alcohol and sexual violence, but it’s not one of cause and effect. There is one way alcohol is a problem, and it’s that it makes it easier for assailants to overpower drunk targets. Alcohol may be used as a weapon, or an excuse for aggressive behavior. But the only thing necessary for a rape to happen is the presence of a rapist.

So what do we do to prevent rapists from attacking, if limiting their alcohol consumption is not enough? Both in the Stanford rape and another case that was in the news recently, everyday heroes showed us that a simple act like speaking up can make a difference.

At Stanford, two men riding their bicycles past the scene of Turner’s assault saw that something was wrong, and they asked, “What are you doing?” At a bar in Santa Monica where a man has been charged with drugging the drink of a woman he was out with, police say bystanders alerted the woman and the bar staff after they saw him put something in her glass.

It’s especially important for bystanders to be prepared to intervene in alcohol-fueled environments like college campuses, bars and clubs, where attackers frequently seek targets.

What would it take for more of us to look out for each other? Training can eliminate some of the barriers to taking action, and it’s catching on around the country. Here in Washington, we run a program called Safe Bars, which trains bar staff to stand up against sexual violence.

Bystander intervention isn’t going to end sexual violence alone, obviously. We need to educate boys and men about healthy masculinity, and equip women and girls with skills to set boundaries and protect themselves from attacks. But we can all work to create a culture where violence isn’t tolerated and where everyone plays a role in making our communities safer.

In a poignant letter to her attacker, the survivor of Turner’s attack wrote, “I sleep with two bicycles that I drew taped above my bed to remind myself there are heroes in this story. That we are looking out for one another.”

We can all be those men on the bikes, the women at the bar. We can speak up when we notice something wrong, even when it’s minor — especially when it’s minor, so we have a chance of interrupting it before it gets worse.

In the words of that brave woman whose life will never be the same: Look out for one another.

Lauren R. Taylor is a self-defense instructor and anti-violence educator based in Washington, D.C. She is also a member of The Washington Post's editorial page staff.